I. Field of the Invention
This invention relates to sheet handling apparatus particularly for use in copying machines. More particularly, the invention is concerned with such apparatus in which sheets are automatically moved in sequence into a registered position on a work surface and then moved out of that position to make way for the next sheet.
II. Description of the Prior Art
Quick and accurate movement of documents to a registered predetermined location and removal of these documents is important in the processing of sheet material as for example in the environment of a copying machine. Thus, in a copying machine, an automatic document handler should not only rapidly move the document onto a platen, but must accurately register that document in a specific predetermined copying position or area to assure the production of a complete and visually acceptable copy. If the document is situated on the platen in a skewed or misaligned position within the area, the copy will reflect this same skew or misalignment and may be incomplete and/or unacceptable to the user. If the original is wrinkled, torn or creased it may not produce good copies and will not be acceptable to the user for a great number of reasons, not the least of which may be unsuitability for subsequent use in a machine or automated processor. Moreover, the automated handler must be able to perform these functions efficiently with a maximum range of paper or material weights as documents copied may vary from light weights such as what is known as "onion skin" in the order of 50 grams per square meter to much heavier weights in the order of 120 grams per square meter.
In order to reduce the incidence of skew it has previously been proposed to register the document against a stop, the document being driven over the platen surface by a belt drive. Particularly good results have been achieved by apparatus as proposed in copending Application Ser. No. 687,062, filed May 17, 1976, now U.S. Pat. No. 4,076,233, and assigned to the same assignee as the present application, in which the belt is narrow relative to the surface and is generally centrally located over the surface whereby in operation the belt engages a generally centrally located portion of a document to move the latter over the surface.
One way of registering a document is to feed the document onto the platen surface and then reverse the document against a stop at the inlet end of the platen surface. This is particularly convenient where the document is ejected at the opposite end of the platen since the stop can readily be arranged so as not to interfere with the document as it is fed onto the platen and thus the stop need not be retractable.
In order to ensure that the document is properly registered it is proposed in copending Application Ser. No. 687.059, filed May 17, 1976, now U.S. Pat. No. 4,043,550, and assigned to the same assignee as the present invention to arrange a baffle over the platen, the baffle being positioned against the registration stop during document registration and raised during entry to the platen of a document and removal of the document therefrom. Further, to permit complete and accurate registration of the document, the belt should desirably be able to slip over the document, even if only for a moment, once the document has engaged the stop. In order to achieve this while providing that the drive positively engage the document to drive it onto and off the platen, it has been proposed in copending Application Ser. No. 687,061, filed May 17, 1976 and assigned to the same assignee as the present invention to reduce the frictional engagement of the belt with the document during document reversal as compared with document advance. A preferred mode of achieving this is described wherein a roller acts on the belt. The roller is mounted on an axle having its opposite ends journalled in inclined slots. When the belt is driven to advance a document on the platen, the axle ends roll down the slots to increase the pressure of the belt on the document. On the other hand, when the belt is reversed to register the document against the stop, the axle ends ride up the slots to reduce the pressure.